1. Field of the Invention
The present invention relates to charge protection circuits, and particularly to a charge protection circuit with a timing function.
2. General Background
Many mobile devices employ lithium-ion batteries in their battery packs. The lithium-ion batteries are likely to be damaged in the event of overcharge, overdischarge, and overcurrent. Therefore, battery packs for lithium-ion batteries are provided with battery protection modules including battery protection circuits that prevent lithium-ion batteries from being overcharged, overdischarged, and overcurrent. Such a battery protection circuit has a field effect transistor (FET) chip serving as an electronic switch that opens in response to overcharge, overdischarge, and overcurrent.
FIG. 2 is an exemplary circuit diagram of a conventional battery protection circuit 100. The battery protection circuit 100 includes a lithium-ion battery 1, a charger 2 and a battery protection module 3. The battery protection module 3 includes a control integrated circuit (IC) 31, a first field effect transistor (FET) switch Q1 (hereinafter referred to as “the first switch Q1”) and a second field effect transistor (FET) switch Q2 (hereinafter referred to as “the second switch Q2”). The control IC 31 includes a charge control terminal Cout (hereinafter referred to as “the terminal Cout”), a discharge control terminal Dout (hereinafter “the terminal Dout”).
The control IC 31 provides an overcharge detection function to turn off the second switch Q2 when an overvoltage is applied to the lithium-ion battery 1 due to some failure during charging, and an overdischarge detection function to turn off the first switch Q1 when the voltage of the lithium-ion battery 1 drops to or below a predetermined voltage.
However, it is difficult to accurately determine whether or not the lithium-ion 1 has been overcharged according to the overvoltage applied on the lithium-ion 1.
Therefore, it is necessary to provide a charge protection circuit with a timing function, which terminates a lithium-ion battery charging process when the charge time reaches a predetermined charge time, thereby preventing the lithium-ion batteries from being overcharged.